1. Field of the Invention
This invention relates to methods and compositions for treating cancer. Specifically, the invention relates to the use of a procytotoxin that can be converted to an acetylated cytotoxin in a tumor-cell specific manner, such that the tumor cell is destroyed by the activated cytotoxin.
2. Background of the Invention
Present methods for tumor treatment, especially for cancer treatment, remain sub-optimal and often are accompanied by severe complications. In fact, virtually all of the known therapies have serious adverse side effects, most often caused by the lack of specificity and thoroughness in the destruction or removal of tumor or cancer cells.
For example, surgery, a common procedure for removing cancerous cells from a patient, is often incomplete, and it disfigures the patient or interferes with normal bodily functions. Similarly, chemotherapy and radiation treatment can indiscriminately destroy normal cells, causing unwanted side-effects while leaving many cancer cells unaffected. Chemotherapeutic agents, especially antimetabolites, while effective to varying degrees against cancer cells that are continuously undergoing or preparing for mitosis, are not effective against cancer cells that are in the resting (G0) stage.
Cancer treatment is most effective when cancer cells can be eliminated as completely as possible from the patient's body. Thus, continuous or consecutive dosages are often administered to the patient. Because most available chemotherapeutic agents are also toxic to normal cells, the dose of cytotoxic drug is adjusted to the limits of tolerance to achieve the maximum destruction of malignant cells, and the interval between doses must be such that the rate of tumor re-growth does not exceed tumor killing. Accordingly, in order to achieve increased efficiency, the chemotherapeutic agents should have high target-cell specificity and high target-cell toxicity or potency.
To this end, the inventors of the present invention previously discovered compositions and methods for treating cancer in a site-specific manner. In particular, U.S. patent application Ser. No. 09/851,422 describes a modified cytotoxic peptide that can be rendered non-toxic by the addition, via a peptide bond, of at least one amino acid residue to the ε-amino group of a lysine residue in the cytotoxic peptide. In the presence of a specific target cell enzyme, the peptide bond is cleaved and the cytotoxic peptide resumes its toxic properties.
But since certain effective cancer treatment methods are, in part, dependent on tumor type and location, and certain treatment methods are more suited for a specific route of administration, there is always a need for additional treatment agents and methods that can be used so as to expand the possible options available for successfully combating cancer. The present invention fulfills these needs and further provides other related advantages.